


Breaking Black

by damnedxfate



Category: Undertale (Video Game)
Genre: Alternate Universe - Swapfell, Alternate Universe - Underfell, Alternate Universe - Underlust, Alternate Universe - Underswap, Anal Sex, Blow Jobs, Bondage, Bondage and Discipline, Creampie, Dom/sub, Double Penetration, Ecto-Genitalia (Undertale), Exhibitionism, Extremely Dubious Consent, Fellcest - Freeform, Gags, M/M, NOT RAPE, Non-Consensual Drug Use, Socket fucking, Swapcest - Freeform, Swapfell Papyrus - Freeform, Swapfell Sans, Underfell Papyrus, Underfell Sans, Underswap Papyrus, Underswap Sans, Voyeurism, Wax Play, minor plain play, swapfellcest - Freeform, underlust papyrus-Sass, underlust sans- Shimmy
Language: English
Status: Completed
Published: 2018-07-01
Updated: 2018-07-01
Packaged: 2019-05-31 17:59:46
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,752
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15124886
Author URL: https://archiveofourown.org/users/damnedxfate/pseuds/damnedxfate
Summary: It was a Papyrus job to help their Sans with their fatal flaw. Black's just happened to be getting the better of him more and more lately. Slim wasn't going to allow it to continue a second longer.





	Breaking Black

**Author's Note:**

> Hello guys! I have been wanting to write this for a while and finally managed to get time in between projects to do so!  
> Please mind the tags and warnings.

Slim was getting really tired of this shit. Master and Mutt had its uses, yes, but only when in Swapfell and in the public eye. At home or in the presence of their counterparts? Black had no right to treat him in such a way.    
  
Slim was the Dom, Slim was the Master, Slim was the one who was rapidly losing his control as he watched his smug little brother sashayed away to rejoin the small group of Sanses in the corner. Which left Slim to rub his stinging cheek surrounded by his alternate selves. All quietly taking in what had transpired.  
  
It was a unspoken but universal truth. All Sanses no matter their personality, submitted to their brothers. The healthier, stronger, more balanced Papyri their doms, their caretakers, their others halves. Never had a Sans dared to sully the sanctity of a private get together in such a way. To not only raise their voice but to ignore their master’s warning, order and then demand to stand down and then to strike him?  
  
There was no excuse for this insult. No pardon for this act.   
  
Slim stood tall, exchanging a loaded glance with the others. The Sanses that had seen the exchange shuddered. Black caught up in his own superiority was oblivious to his impending punishment.   
  
And **he would be punished**.

* * *

  
“Come down Bro, dinners done” Slim called out from the kitchen calmly. It was his turn to cook. Their Kitchen wasn’t big enough for them to eat there so usually they took their plates to the living room and ate while watching the television. This gave Slim enough privacy to enact the first step of his plan to bring order and stability back into their relationship.   
  
It had been a couple of weeks since the ...incident… at the multiverse get together. It had taken him this long to have everything set up and in place. Deals struck, toys ordered, flyers sent out. Time he sorely needed to cool down and take a calmer mindset lest he lost himself during the upcoming scene.    
  
Whistling merrily Slim uncorked a bottle he pulled from his pocket. The liquid inside had a similar consistency to water but held an ominous sheen as if oil had been mixed in. Upending the bottle over the food, enchiladas Black’s favorite, the contents absorbed quickly dispersing in the sauce. His little brother would eat up every last little bite of the enchilada without thinking twice about its contents. Slim had never given Black a reason to distrust him at least until now.    
  
“Finally! One Would Think You Were Trying To Kill Me From Starvation” Black snapped at him without so much as a hello. They had spent the entire day working their asses off and keeping up pretenses yet at home they were supposed to be themselves. Black seemed to forget that more and more every day. Any regrets Slim might of still had evaporated instantaneously at the rude tone.    
  
“Enjoy bro” Slim shrugged. He knew the drug would work. Green, the Gaster Papyrus, mixed this sleep inducing drug himself at Slim’s request. It was strong enough to keep any one of them out for a few hours. For one of Black’s size? Slim would have plenty of time to set up. For now he ate his food without a care in the world keeping an eye trained on his smaller brother.    
  
Each spoonful rose slower than the last. Until the spoon slipped gently from slack fingers and Black slumped forward into Slim’s waiting arms.    
  
Time to get this show on the road.   
  


* * *

 

  
Overhead lights snapped on with stoic click illuminating the instruments below that had been arranged with an almost clinical precision. Each item lovingly placed to fulfill its purpose. At the center proudly stood a behemoth of wood, metal and treated leather.   
  
Shaped like a capital X, a Saint Andrew’s cross, faced a multitude of cameras connected by cords to a large screen television and computer. At its sides stood cloth covered tables hiding their contents from view.    
  
Two figures, one standing while carrying the other bridal style, the cause for the sudden lighting approached the large mount. Stepping on one the hidden pedals brought the contraption to a horizontal position where the larger monster lovingly placed the other down.   
  
“There we go baby bro, nice and comfy” Slim murmured as if his brother was only sleeping and not drugged out of his mind. Whistling merrily as he divested his brother of his clothes while arranging him spread eagle like a virgin sacrifice before a primordial god. Padded leather cuffs were tied to each wrist and ankle firmly along side a heavy leather collar complete with D ring on the front. The cuffs wouldn’t block Black’s magic. They had safe words and tap outs but if Black really wanted out he could ask for it nicely.   
  
With an unnecessary flourish, Slim pulled a blanket off one of the side tables before dropping the fabric to the floor. “Damn I owe Sass a huge favor after this”, set on the table were all kinds of brand new toys for play from the Underlust Papyrus’s new line. While yes, Slim and Black had their own well loved toys, it would look much better on the big screen if they used sparkly new products that weren't quite released to the public yet. The fact that they would promote Sass’s new line of products didn’t hurt either since Slim would be getting a nice cut out of it.    
  
First thing first was a gag for Black’s pretty little mouth but which one? Running a finger across the shiny red ball of one he decided to use the last one in the line up. An “O” gag with plug. It would keep his brother’s mouth nice and wide so that everyone could see his wiggling tongue and then hear his cries of passion but the plug would help keep him quiet until Slim felt like releasing him. Another form of control to further cement his dominant position to his arrogant little “lord”. The click of metal on bone echoed eerily around the dead silent room while he adjusted its form around Black’s head and mouth.    
  
‘ _ No tongue yet _ ’ he thought to himself with a physical huff of displeasure afterward staring at the open mouth before sealing it with the plug. That’s fine for now. Turning back to the table he grabbed a neat bundle of ooblong beads the size of his thumb. Bullet vibrators, wireless, and a roll of clear tape. He set each one on his brother’s erogenous zones. Those little spots that made the other weak in the knees and wet between the legs. His neck and clavicle, small almost dainty ribs, his ilium, sacrum and cheekily one right on the inside of his pubic symphysis. When his magic formed it would have no choice but to form over this specific bead trapping it quite firmly against the cartlidge. The vibration would run through the magic flesh igniting the nerves from the inside.    
  
He gave Black a once over. Chains? Check. Gag? Check. Toys? Check. All that was missing was his brother to wake up and the fun to begin. All though...it wouldn't hurt if he got one more thing or two ready.    
  
From his pocket he pulled another vial. The liquid inside this one a bright luminescent silver which he placed on the same little side table along with a unused and sealed syringe. That was for after introductions. His own special mix this time.    
  
Walking over to the only chair in the room situated by the computer screens he began to adjust the equipment while he waited for the drugs to wear off. Which would be any minute now if he timed it right~

* * *

  
“Mmm...hm? HMNF!” the sleepy moans woke Slim form his light doze. The following angry shrieks told him it was show time. Flicking a switch on the panel before him acted as a catalyst turning on all the cameras and starting the stream. Hundreds of eyes were waiting for the show after all.    
  
“Morning Bro, took you long enough sleeping beauty” Slim called walking into both Black’s and the camera's line of sight.    
  
“UNF! PARR!” Black tried to yell around the gag but when that did little good he continued to kick and flail as much as the shackles would let him. He hadn’t missed the camera or the implements around the room but was far too furious to care. How dare Slim do this to him.    
  
“Welp as you can plainly see. Black, my Sans, has decided that he no longer wants to obey the sanctity of our union. He feels that I as his brother, his dom, and his balance am now below him and worth little to nothing in his eyes” Slim started his introduction facing the camera and sparing the bare minimum of attention to the other. “Sooo, I have decided to remind him of his place….forcefully. Little Black here has a bit too much pride in him so let's see how he feels after half the multiverse has seen his cute little face while hes being fucked open” With a grand flourish Slim kicked the pedal once more bringing the mount back to its original vertical position.    
  
“Let the show begin”   
  
“Nnnmf!”   
  
Walking around Black he grabbed a small pink remote of the table holding it up for all to see. “Sass brand multi purpose wireless remote. With just a flick” Here Slim fiddled with the set of knobs adorning the front. “You can control a full set of bullet vibrators at individual speeds” The resulting scream told him Black hadn’t noticed the addition to his bones. The little bullets quaking rapidly or gently depending on their setting, stimulating hot spots.   
  
Resting his chin on his hand a moment to enjoy the show. Black’s head was thrown back in surprise his legs stiff. His hips jittering back and forth to both escape and get more of the stimulation. Slim left him there a moment while he wheeled over the next covered table. Sliding this cloth off showed off his next tray of toys. Perfect for edging his brother.    
  
Lighting a candle with a promise of later to the inanimate object Slim picked his first toy. A long soft feather. Not many knew but Black was actually extremely ticklish.    
  
“Now bro how about you be a good boy and summon something for me to play with? You know what I want. Show the boys your cute little pussy” Slim called as he walked over hiding the feather from view.    
  
“Fngk mru!” How Black managed to snarl or even form what was clearly ‘Fuck you’ with his mouth held wide open was a feat in itself. He really shouldn’t be surprised, Black had the biggest mouth out of any Sans. Not even Shimmy the underlust Sans could keep up hell even Red a complete cock slut (When Edge was in the rare mood for a threesome or a show. Over protective bastard) could take what Black could.   
  
Slim could only sigh and look toward the camera with a “See what I mean?” Black just never took the easy way. He always had to kick, scream and punch. Now it's fine being a brat every once and awhile. Always fun times slapping Black’s ass while he's balls deep inside him but it's no fun if its actual punishment. Brat taming not bitch wrangling thank you very much. 

 

Bringing the feather up in clear view Slim twirled it laughing slightly at Black’s horrified face. Wide purple eye lights flickering from the brightly colored feather to the camera pleadingly. His reputation would be ruined if they found out! Black strongest of the Sanses, Captain of the Swapfell Royal Guard to be ticklish? Absurd he would be a laughing stock! The feather was slid across his left floating rib and then the other just so before Slim began to flick it rapidly side to side and up and down. Black’s high pitched squeal transforming into garbled laughter. Tears started bead and then track down his face either from the laughing or humiliation.    
  
“Ain't he cute folks? My little bro the feather weight~” Even with his teasing Slim kept a careful eye on his brother. Taking the toy away when Black’s breathing started to stutter harshly. Stepping away long enough for Black to recover, Slim gave him an appraising eye. There was magic swirling low in his pelvic girdle but nothing else. Black was being stubborn. Again.   
  
Huffing he tossed the feather none too gently on the tray before grabbing the aforementioned candle. Giving it a swirl to see how much melted wax  had collected. Not quite enough yet. Slim grabbed a short crop as well.    
  
Again he turned back to the camera and presented his goods.   
  
“Black just doesn’t wanna be a good boy guys. I asked him nicely but here we are anyway. Now I know some of you guys got your own badly behaved subs. I learned that sometimes you gotta mess with them a bit. A little good, a little bad and well if that doesn’t work you just gotta  break them in” Slim’s sentence probably sounded worse then it was but they all knew the truth even Black. No Papyrus would seriously harm their Sans so what did he have as a backup plan? Black didn’t want to know but his fool’s pride wouldn’t let him back down.   
  
He formed a cock instead.   
  
“HAAHNG!” Black couldn’t have hope to contain his scream when the crop whipped cruelly over the tip of his magic the moment it formed. Slim had anticipated his act of defiance. The sting of the crop transformed into the burn of hot wax being dripped on the same spot. Black tried to curl his legs inward anything to cover his much abused magic.    
  
“Well, guess I have no other choice” With a longing look Slim blew out the candle, setting it and the crop back on the table. He had truly, deeply, hoped that Black would of seen some sense but no. He just had to dig his heels deeper. Slim didn’t like having to do this but they had seen what happens to a Sans without their Papyrus. The verse breaking destruction didn’t need any explanation. Slim would be damned if he let Black go down that road. He loved him far too much.    
  
Slim didn’t make eye contact with his brother when he reached into the heaving chest cavity to pull out that beautiful but rapidly beating SOUL. He had wanted to avoid this. Exposing the culmination of his brother’s entire being to the cameras but it was necessary for the next step. Slim did afford him some modesty by cupping it in his hand so that most was covered by his long phalanges.    
  
Black held his breath while Slim was handling his SOUL. He could feel the intent, Slim would never hurt him. But Black refused to back down, he wouldn’t tap out, though he knew even then that Slim would honor it. He kept up his glare.   
  
Slim held up the bottle from earlier.    
  
“Not many of you know but I have dabbled a bit in chemistry” He began. “Specifically both the scientific and magical composition of a monster’s body. I made this some years ago just to see if I could” Slim swished the bottle while he remisced. “This will amplify all sensation to conjured magic. The intangible nerves firing rapidly at the slightest touch. Like a controlled heat you’re fully conscious during” he loaded the syringe with the bottles full contents steadfastly ignoring the slew of curses being thrown at him from behind him. With a plunge the needle was inserted into the pulsing soul releasing its contents.   
  
“You’ll get to see the results now and yes before you ask I may be persuaded to give you a vial or two” Slim tossed a wink at the camera placing the used syringe on the tray and grabbing a small leather contraption by it. A special cage for the SOUL. Similar to a cock ring but it cut off more than just penile ejacualtion. Black wouldn’t be able to orgasm from anything he formed until the cage was removed. “Be a good boy baby” Slim reached over loosening the ring gag so it slid down and placing the SOUL back where it belonged. He needed to sit down. He knew he needed to do this but damn he didn’t want it like this.   
  
“I’LL KILL YOU FOR THIS! HOW DARE YOU! I AM BETTER THAN YOU! I AM BETTER..than..all of you...hah” Black’s angry tirade cut off mid way through. The Serum had already started to work its way through his system. Slim turned off all the vibrators. Let Black experience it without any outside influence.    
  
It was surely an experience to watch.   
  
Sweat began to trickle down quickly heating bones. Faint tremors knocking them loose so they slid down in tantalizing trails. The small swirls of magic that occupied the pelvic cavity before grew darker, twining itself up ribs and down shaking femurs. Knees bowed inward, dainty wrist and ankles shivering, rattling their shackles. With a snap of displaced air brightly glowing magic manifested beyond that of the original phallus.    
  
“What have you-mnyaah...what have you done to meee?” Black slurred panting. Everything,even the slight shifting of the air in the room felt like fire on his skin and bones. He didn’t even realize when he started presenting. Angling his hips outward while spreading his legs from their curved position. He didn’t even care that his erection had dissolved into wet lips. Juices bubbling out to slide wetly down his thighs over the curve of his ass. He looked up pleadingly at his brother showing off teary heart shaped eyes.   
  
“Papy…?”   
  
“Oh fuuuuck” Black hadn’t called him that nickname in years. Truthfully, Slim got jealous every time his Swap counterpart’s little Sans would mewl that childhood nickname in that voice so similar to Black’s.    
  
Slim couldn’t hold himself back a second more.    
  
Flicking the vibrators to a random setting he reached forward rasping his claw tips down quaking femurs to clasp knees and spread them wider. They snapped open without barely a nudge from him. Licking two of his fingertips, Slim brought them down to roll Black’s swollen clit while he latched on to Black’s neck with his teeth and tongue.    
  
“Mweh Papy harder papy ple-aaahan!” Black was cut off with a scream with those teasing fingers jabbed into his core. Roughly jolting his body at a rapid uneven rhythm. Legs kicking slightly Black tried to find purchase on the floor to shove himself down on the fingers.    
  
“You look so good like this Baby bro. Taking my fingers up your pretty cunt” Slim cooed in between licks to the bitten vertebrae. “You like when I take care of you right? When I make you feel good? Like you asked me to?” He brought up that night so long ago. Their very first night together. They had spent it in each other’s arms talking, promising each other, pledging themselves to one another.    
  
“I asked hng you to be my DOG! Haaah!” Black snapped at him both verbally and physically. Slim felt the sharpened teeth rasp the side of his face even as he pulled back. Even with his body throbbing in heat, even with his SOUL screaming at Slim to help him, Black still couldn’t admit it out loud that he had gone way over his head.    
  
“I got you bro” sighing Slim hooked a finger into Black’s eye socket ignoring the indignant howl and slipped the ring gag backup forcing those snapping jaws wide open again. Pulling his hand back, Slim kicked a second pedestal bringing the mount forward at a 90 degree angle causing Black’s open mouth to be level with Slim’s crotch. Slim wasted no unbuckling his pants and pulling out his erection.   
  
Thick and pierced the turgid flesh hung heavily in his hand. Pre cum already oozed freely from the head in clear glistening strands. Giving himself a couple of strokes to spread his click he slapped a hand on the back of Black’s skull and shoved himself down to the base with a heavy groan.    
  
Black choked at the sudden intrusion before he summoned his tongue and throat to accommodate the girth. Coughing when Slim pulled back only to slam inside again. With long, deep strokes Slim took his pleasure for the warm mouth. Humming mockingly when moans started to reverberate around his cock. Black’s face screamed defiance but his tongue was curling around him like a snake. Not a single drop of orange magic was escaping Black’s greedy mouth. For someone who screamed dominance he was taking Slim’s cock with the skill only a submissive could cultivate.    
  
“Let me explain something” Slim struggled to sound nonchalant but he couldn’t show weakness. “Black and I are in a dominant and submissive relationship, a “hardcore” one as some of you have called it. It's an equal partnership and we both give and take from each other” Slim held himself inside Black for a moment grinding his hips against the fluttering tongue. “Black needs to let go and I need control. He's got a pride problem. I just don’t give a fuck. So when he bites off more than he can chew, big brother handles it. Now when Black decides HE wants to be the big brother” Slim pulled out to slap himself across the drooling, trapped mouth. “I gotta fix it”   
  
Pulling back to adjust himself Slim angled his cock toward one of Black’s eye sockets. One of their guilty pleasures and another one of Black’s biggest kinks. Inside their skulls was a condensed ball of magic. To feel the sexual intent of Slim’s cock inside his head drove Black out of his mind with pleasure. Many found it too invasive but not them.   
  
This time Slim slide inside gradually, pausing every time Black’s garbled moans grew into a high pitched whines until he was fully seated. The swirling mass of ‘Black’ that coated him was a unique sensation. Like butterfly wings fluttering over his cock. Cold and hot in random flashes. Much gentler from before he started to flex his hips back and forth. Black hung limply in his binds, hips still twitching unconsciously. Moans slipped out of his open mouth as he slowly slipped further into his space. Slim felt so good inside him. The memory of their confessions and pledge in the forefront of his mind now at the reminder.   
  
He had hated what he was doing. Black knew he was going in over his head but the attention felt nice. He felt so strong when he got his big brother to do what he wanted. Black felt like the strongest Sans and by dominating his brother, even stronger then the Papyri. He had broken his promise and was too prideful, too imperious to stop.    
  
He let go of the knot inside with a mewl of surrender.    
  
Slim felt the release deep inside their bond. “Are you ready to be a good boy for me?” he queried. Slim grinned when the resulting nod caused Black to jerk his own skull on Slim’s cock. He pulled back, easing himself out of Black’s socket and brought the mount to its standing position once more.   
  
Murmmuring praise while he undid the binds and ring gag Slim brought Black up into his arms and carried him like a doll until they stood facing the cameras. Just incase Black relapsed, he had to bring the lesson home. Give Black a different kind of attention to bask in from the other’s that wouldn’t jeopardize their bond again.    
  
Spreading Black’s legs, Slim impaled him down to the root starting a harsh pace.   
  
“PAPY HAAAHN YES! PLEASE PAPY” Black’s arms came up to hook around the back of his neck. Black’s magic was like coming home after a long absence. The warm walls pulling him in deeper. Embracing his hard shaft in a tight lover’s hold. The intent of the magic echoing it’s owner’s mantra of more.    
  
Droplets of their combined fluid splashed loudly with each inward jolt. Black’s sharp phalanges scrapped at the base of his skull. The pain zinging down his spine enhancing his pleasure. Extending his tongue Slim licks up the side of Black’s purple kissed cheek before plunging into the wide open mouth muffling his loud wails. Black’s walls fluttered in pseudo orgasms. So close but unable due to the restricting cage.    
  
Slim couldn’t help but to tease him more. Pulling out, ignoring the muffled whine of protesting reverberating around his tongue, he focused his magic. His cock pulls apart forming two smaller but still thick wet shapes. He wastes no time plunging one back into Black’s sopping pussy while the other starts its forceful cleave into his puckered ass.   
  
“Sh-shit!”   
  
“AHG! HAH!”   
  
Thick globs of cum pump out of Slim from the dual simulation painting Black’s insides a bright sienna. Black’s discordant scream of dissatisfaction drowning out his curse. Resting his skull on Black’s shoulder while he pumped his hips slowly enjoying the dredges of his orgasm.   
  
“Sorry baby bro couldn’t help myself~” Releasing one of the slightly spasming legs, Slim brought his hand up passed the palpitating entrance to an engorged clit. Rubbing it in tight little circles. Black did look good like this. Blasted out of his mind from pleasure with his little tummy slowly filling with Slim’s cum. Bringing his sticking fingers away from the swollen bead he cupped Black’s face and turned its.    
  
Black looked destroyed. His mouth hung open, little purple tongue limp and dangling. Eyelights blown wide their form undefined and hazed. Black wasn't even holding on to him anymore, his arms hanging uselessly at his sides with his full weight support by one of Slim’s arms and both of his cocks.    
  
“You ok Sans?” had he gone too far?   
  
“Papy please cum inside me more, make me yours…” Black whimpered softly. “Love you pa-hah-py. Sorry, so sorry. Thank you, thank you, thank you...please cum now?” There was no pride left in those eyes. Only love and hope. Those were his brother’s eyes not the prideful facade he had trapped himself in. It took all of Black’s energy to beg for his Papyrus. But it took nothing for Slim to give in.   
  
Bringing them to the floor for purchase brought the camera down with them. Pinned under Black’s chest the viewers got a clear view of the still trapped soul. Engorged from the trapped magic accumulated from denied orgasms. They saw nicotine stained fingers scrambling around the locks before they were undone with a click. High pitched screaming causing static through their speakers while great globules of purple coated the lense and distorting their view.  The viewers could still see the two silhouettes jerking rhythmically, hear the cries of pleasure with the solid smacks of connecting flesh.    
  
Across the multiverse there were Papyri and Sanses undulating in rapture to the video. Some cooing at their counterparts happiness, others talking long into the early hours of the morning bodies entwined. Confessing all their wrongs and woes to each other. Some still worried by the calculating gleams that had yet to leave their Doms eyes at the sight of the serum.    
  
None of this mattered to Slim or Black. They were lost to all but each other. Bodies aching from over stimulation but refusing to stop. Not enough, not yet, still more.

* * *

  
  
Things subtly changed at the multiverse meetups. Black was still a brat and lorded his prowess to the other Sanses but was respectful. They had talked soul to soul afterward. Black swaddled in blankets and Slim’s arms while he slowly sipped water. They reviewed their past promises, making new one, new pledges. Their bond was stronger then ever.    
  
The off hand comments, casual flirts, or even propositions were answered with either sneers from Black or good natured rebuffs from Slim. Maybe eventually they wouldn’t mind a threesome, the Swaps were mighty cute, but right now it was almost like a honeymoon stage. The moment they were alone, clothes was thrown off and Black submitted to the only one that mattered to him. Slim was more than happy to show his brother just how much he loved him. Just how far he would go for him. 

**Author's Note:**

> If you liked it please take a moment to give a kudos and/or comment please? It really helps encourage me!


End file.
